Malignant brain tumors, either primary or secondary to systemic cancer, remain a tremendous challenge in clinical oncology because of the limited utility of currently available treatment options. The increasing frequency of neoplastic disease of the central nervous system urgently calls for novel experimental therapeutics improving the outlook for affected patients. We have developed a promising new therapeutic modality directed against malignant brain tumors based on poliovirus recombinants devoid of pathogenic properties. A candidate oncolytic poliovirus recombinant for the treatment of malignant glioma is being prepared for production for Phase-I clinical trials. Our approach is based on mechanisms of viral gene expression to direct viral replication and cell killing specifically to tumor cells. Through genetic manipulation of a poliovirus translation control element, we achieved specific targeting of tumor cells for destruction by replicating virus. We plan to conduct experiments to identify the role of eukaryotic factors associated with brain tumors and tumor specific viral cytotoxicity. Isolation of cellular factors responsible for targeting of tumor cells and the characterization of the molecular mechanism of their action will help to identify tumor types likely to respond favorably to our treatment. Furthermore, the elucidation of the mechanisms responsible for selective tumor cell killing by oncolytic polioviruses will make this principle applicable in novel ways. Recently, improved forms of delivery for macromolecules to the human brain have been developed. To optimize treatment conditions of our agent in upcoming clinical trials, we will perform comprehensive evaluation of alternative means of administration of our agent in a rat brain tumor model. In addition, we will analyze the therapeutic potential of our treatment against neoplastic meningitis, an increasingly common CNS complication of systemic cancers, in a rat tumor model. Using our insight into mechanism of tumor-specific viral replication, we will construct recombinant alpha-Herpesviruses replicating under control of poliovirus regulatory 5' non-translated sequences. We are aiming to generate a novel prototype of oncolytic virus based on highly attenuated Herpesviruses with tumor-specific replication profiles.